Implantable medical device coils

ABSTRACT

An implantable medical device (IMD) may include a plurality of coils that may be used to recharge a power supply of the IMD and/or provide telemetry for the IMD. The IMD may be configured to couple all of the coils in series, such that currents that are induced by each of the coils are added together when the IMD is exposed to an electromagnetic field. The IMD may be configured to alter the coupling of the coils such that the coils are coupled in series opposition, such that currents that are induced by some coils of the IMD are opposed by currents that are induced by other coils of the IMD.

TECHNICAL FIELD

The disclosure relates to coils for use with implantable medicaldevices, e.g., for wireless communication or charging.

BACKGROUND

Medical devices may be external or implanted. Implantable medicaldevices (IMDs) may serve a wide variety of functions, such as sensingone or more parameters of a patient, delivering one or more therapies tothe patient, or a combination of these and other functions. An IMD maydeliver therapy to, and/or monitor a physiological condition of, avariety of organs, nerves, muscles, tissues or vasculatures of thepatient, such as the heart, brain, stomach, spinal cord, pelvic floor,or the like. The therapy provided by the IMD may include electricalstimulation therapy, drug delivery therapy or the like.

The IMD may include a power source such as a battery. The power sourcemay be configured to provide power for the IMD to execute the functionsfor which the IMD was designed. In some examples, the power source maybe rechargeable. The power source may be rechargeable through the use ofcoils that are configured to induce a current that is then channeledinto the power source.

The IMD may also transmit communications to and/or receivecommunications from another device via wireless telemetry. The IMD maytransmit and/or receive communications with another device that isimplanted, attached to (e.g., worn by) the patient or otherwise locatednear the patient, or remote from the patient. The communications mayinclude information related to a condition of the patient, such asphysiological signals measured by one or more sensors, informationrelated to a therapy delivered to the patient, or information that maybe used to control or configure a therapy to be delivered to the patientor physiological signal measurement. The IMD may transmit and/or receiveinformation using any of a variety of wireless communication techniques,including inductive telemetry, magnetic telemetry, radio frequency (RF)telemetry, or the like.

SUMMARY

Aspects of the disclosure are directed to coils of the implantablemedical device (IMD) that are used to, for example, recharge a batteryor other power source of the IMD and/or provide telemetry for the IMD.The coils may be configured to transmit or receive signals for the IMD,e.g., induce a current that may then be channeled into a power source ofthe IMD. The IMD may be configured to electrically couple all of thecoils in series, such that currents that are induced by each of thecoils are additive in relation to each other when the IMD is exposed toan electromagnetic field. The IMD may be further configured toelectrically couple the coils in series opposition, such that currentsthat are induced by some of the coils of the IMD are opposed by currentsthat are induced by other of the coils of the IMD, such that a currentthat is induced by the coils of the IMB is at least partially cancelled.A switch of the IMD may alter a coupling of the coils from series toseries opposition in response to determining that the coils are inducingmore current than desired, such that the IMD is overheating or isotherwise inducing undesirably high voltages (e.g., that may overchargea respective battery). In this way, the IMD may be configured to usecoils that may recharge a battery or provide telemetry for the IMB whilealso being configured to be exposed to the relatively intenseelectromagnetic fields of various electromagnetic interference (EMI)sources, such as magnetic reasoning imagining (MRI) machines, withoutinducing an amount of current or voltage that may cause adverse effectsto the IMB or the patient.

In other examples, aspects of the disclosure relate to an implantablemedical device that includes an implantable medical housing, aprocessing circuit within the implantable medical housing, a first coilthat is configured to wirelessly receive a signal and is secured to theimplantable medical device, a second coil that is configured towirelessly receive the signal and is secured to the implantable medicaldevice, switching circuitry within the housing, and a sensor. Theprocessing circuit may be configured to cause the switching circuitry toselectably couple the first coil to the second coil in either series,such that the first coil is coiled in a same direction as the secondcoil, or in series opposition, such that the first coil is coiled in theopposite direction as the second coil. The sensors sense a parameterthat indicates a magnitude of an induced current that is induced overthe first coil and the second coil as a result of receiving the signal.The parameter is at least one of temperature, voltage, or current.

In other examples, aspects of the disclosure relate to a method ofmanaging coils of an implantable medical device. The method includescoupling by a switching circuit, as caused by a processing circuit ofthe implantable medical device, a first coil that is secured to theimplantable medical device to a second coil that is secured to theimplantable medical device in series such that the first coil is coiledin a same direction as the second coil, wherein both the first coil andthe second coil are configured to wirelessly receive a signal. Themethod further includes receiving, by both the first coil and the secondcoil, the signal. The method further includes detecting, by theprocessing circuit, that a parameter that indicates a magnitude of aninduced current that is induced over the first coil and the second coilas a result of receiving the signal surpasses a predetermined threshold.The method further includes coupling, by switching circuitry of theimplantable medical device as caused by the processing circuit, thefirst coil and second coil in series opposition such that the first coilis coiled in the opposite direction as the second coil.

In other examples, aspects of the disclosure relate to an implantablemedical device comprising an implantable medical housing, a processingcircuit within the implantable medical housing, one or more leads thatare configured to extend from the implantable medical housing and beimplanted into a brain of a patient, one or more electrodes at a distalend of the one or more leads that are configured to deliver electricalstimulation to the brain of the patient, a stimulation circuitconfigured to generate the electrical stimulation, a power supply thatis configured to provide power for the generation of the electricalstimulation, switching circuitry that is electrically coupled to theprocessing circuit, a first coil that is coupled through the switchingcircuitry to the power supply and configured to wirelessly receive acharging signal, a second coil that is coupled through the switchingcircuitry to the power supply and configured to wirelessly receive thesignal, and a sensor. The processing circuit is configured to cause theswitching circuitry to selectably couple the first coil to the secondcoil in either series such that the first coil is coiled in a samedirection as the second coil or in series opposition such that the firstcoil is coiled in an opposite direction as the second coil. The sensorsenses a parameter that indicates a magnitude of an induced current thatis induced over the first coil and the second coil as a result ofreceiving the signal. The parameter is at least one of temperature,voltage, or current.

The details of one or more example are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a conceptual and schematic diagram illustrating an examplesystem that includes an implantable medical device (IMD) and a leadimplanted into a brain of a patient.

FIG. 1B is a conceptual and schematic diagram illustrating an examplesystem that includes an implantable medical device (IMD) and a leadimplanted near a spinal cord of a patient.

FIG. 2 is a conceptual and schematic block diagram of the IMD of FIGS.1A and 1B.

FIGS. 3A and 3B are conceptual and schematic diagrams of two coils of anIMD being coupled in series and series opposition, respectively.

FIGS. 4A and 4B are conceptual and schematic diagrams of three coils ofan IMD being coupled in series and series opposition, respectively.

FIGS. 5A-5E are conceptual and perspective views of coils mounted on thehousing of an IMD, coils for stacked mounting on a frame, coils fornested mounting on a frame, a coil printed on a surface of an IMD, andtwo coils of an IMD, respectively.

FIG. 6 is a flowchart depicting an example method of coupling two coilsin series and series opposition.

FIG. 7 is a flowchart depicting an example method of coupling three ormore coils in series and series opposition.

DETAILED DESCRIPTION

This disclosure is generally directed to coils of an implantable medicaldevice (IMD) that is used to monitor a parameter of a patient and/ordeliver a therapy to a patient. The IMB may include two or more coils.The coils may be used to recharge a battery or power source of the IMD,or otherwise to receive power from an external power source (e.g.,through inductive coupling). Alternatively, and/or additionally, thecoils may be used as an antenna to transmit or receive wirelesscommunication signals. The IMB may be include a switch (hereinafterreferred to as “switching circuitry”) that alters the manner in whichthe coils are electrically coupled to components of the IMD. Forexample, the IMB may include two substantially similar coils that theswitching circuitry may electrically couple in series. When coupled inseries, the two substantially similar coils may each inducesubstantially similar currents that are then combined and channeled intoa power source of the IMB. The switching circuitry may also electricallycouple the two coils in series opposition, such that the twosubstantially similar coils may induce substantially opposite currentsthat, in some examples, effectively cancel each other.

FIGS. 1A and 1B are conceptual diagrams illustrating example systems 10Aand 10B (collectively “systems 10”) that includes implantable medicaldevices 12A and 12B (collectively “IMDs 12”), each of which includeswith internal coils 14. IMDs 12 are depicted as implanted in patients16A and 16B (collectively “patients 16”). IMDs 12 may deliver therapyand/or monitor patients 16 using electrodes 22A, 22B, 22C, 22D(collectively “electrodes 22”). For example, in FIG. 1A, medical system10A includes an IMB 12A configured to deliver therapy to and/or sensingphysiological signals from brain 18 of patient 16A through lead 20A.Specifically, IMD 12A includes lead 20A entering through a cranium ofpatient 16A and implanted within brain 18 of patient 16A to deliver deepbrain stimulation (DBS). One or more electrodes 22A, 22B at distal end24A of lead 20A provide electrical pulses to surrounding anatomicalregions of brain 18 in a therapy that may alleviate a condition ofpatient 16A. In some examples, more than one lead 20A may be implantedwithin brain 18 of patient 16A to stimulate multiple anatomical regionsof the brain.

DBS may be used to treat dysfunctional neuronal activity in the brainwhich manifests as diseases or disorders such as Huntington's Disease,Parkinson's Disease, or movement disorders. The exact reasons whyelectrical stimulation therapy is capable of treating such conditions ofthe brain is unknown, but symptoms of these diseases can be lessened oreliminated with electrical stimulation therapy. Certain anatomicalregions of brain 18 are responsible for producing the symptoms of suchbrain disorders. As one example, stimulating an anatomical region, suchas the Substantia Nigra, in brain 18 may reduce the number and magnitudeof tremors experienced by patient 16A. Other anatomical regions mayinclude the subthalamic nucleus, globus pallidus interna, ventralintermediate, and zona inserta. Anatomical regions such as these aretargeted by the clinician during the implantation of lead 20A. In otherwords, the clinician may attempt to position the distal portion of lead20A, including electrodes 22A, 22B, as close to these regions aspossible.

IMD 12A may include two or more internal coils 14 that are configured tocreate or cancel one or more induced currents as a result ofelectromagnetic fields. For example, IMD 12A may include power source 26that is configured to produce power for IMD 12A to deliver electricalstimulation and/or detect electrical signals, and recharge coils 14 maybe coupled in series by IMD 12A to recharge power source 26 in responseto an electromagnetic field created by charging device 28, e.g., whencoils 14 act as recharge coils. In some examples, IMD 12A may beconfigured to transmit signals to or receive signals from programmer 30,e.g., when coils 14 act as telemetry coils when coils 14 are coupled inseries.

Further, in either or both cases, IMD 12A may be configured to modify acoupling of coils 14 such that some of coils 14 are electrically coupledin series opposition in relation to others of coils 14, thereincancelling a total induced current of coils 14. For example, IMD 12A maycouple coils 14 in series opposition when patient 16A undergoesmagnetic-resonance imaging (MRI) testing, to reduce or eliminate achance of a relatively high current being induced by coils 14 of IMD12A. By configuring IMD 12A to have a capability to couple coils 14 inseries opposition, IMD 12A may have an increased ability to regulate atemperature of IMD 12A and/or the tissue of patient 16A surrounding IMD12A. Though depicted as separate components for the sake ofillustration, in other examples the functions provided by chargingdevice 28 and programmer 30 may be provided partially or entirely by asingle component. Additionally, it is to be understood that the depictedlocation of coils 14 and power source 26 within IMD 12A is for purposesof illustration only, as coils 14 and power source 26 may be locatedwithin or about IMD 12A at many locations in many orientations.

In the example of FIG. 1B, system 10B includes IMD 12B that may beconfigured to deliver therapy to and/or sense physiological signals fromtarget tissue. The target tissue may include or be near spinal cord 32and/or pelvic nerves 34 (e.g., a pudendal nerve or sacral nerve), or anyother nervous or muscle tissue that may be stimulated or from whichphysiological signals of patient 16B may be sensed through lead 20B.More particularly, IMD 12B may deliver electrical stimulation and senseelectrical signals via electrodes 22C, 22D at distal end 24B of lead20B. IMD 12B may provide stimulation to treat symptoms of patient 16B,such as pain, fecal or urinary incontinence, erectile dysfunction, orother sexual dysfunction.

IMDs 12 may include electronics and other internal components necessaryor desirable for providing the functionality described herein as beingassociated with the device. In one example, IMDs 12 include processingcircuitry, memory, signal generation circuitry, sensing circuitry, and atelemetry circuitry. In general, memory of IMD 12 may includecomputer-readable instructions that, when executed by a processingcircuit of the IMD, cause it to perform various functions attributed tothe device herein. For example, the processing circuit of an IMD 12 maycontrol the signal generation circuitry and sensing circuitry accordingto instructions and/or data stored on memory to deliver therapy topatient 16, sense physiological signals of patient 16, and perform otherfunctions related to treating one or more conditions of patient 16 withIMD 12.

The signal generation circuitry of IMD 12 may generate electricalstimulation that is delivered to patient 16 via electrodes 22 on one ormore leads 20, in order to provide, for example, DBS, spinal cordstimulation, or other neuromodulation (e.g., neurostimulation). Thesensing circuitry of IMD 12 may monitor electrical signals fromelectrodes on leads 20 of IMD 12 in order to monitor electrical activityof the patient, e.g., to monitor electrical signals generated by brain18, or other neurological signals or action potentials. Telemetrycircuitry of IMD 12 may include any suitable hardware, firmware,software or any combination thereof for communicating with anotherdevice, such as programmer 30. Under the control of a processing circuitof IMD 12, the telemetry circuitry may use coils 14 to receive downlinktelemetry from and send uplink telemetry to programmer 30.

Programmer 30 may be a handheld computing device, computer workstation,or networked computing device. Programmer 30 may include electronics andother internal components necessary or desirable for executing thefunctions associated with the device. In one example, programmer 30includes one or more processing circuits and memory, as well as a userinterface, telemetry circuitry, and power source.

In other examples, IMD 12 may be used for other forms of treatment ormonitoring. For example, IMD 12 may be implanted near a heart of patient16 and be used to provide therapy to the heart or monitor a parameter ofthe heart. In this example, IMD 12 may be configured providedefibrillation therapy to the heart or otherwise provide electricsignals to or read electrical signals from the heart. Other examples ofIMD 12 being implanted in different areas of patient 16 to providetherapy to or monitor different areas of patient 16 are also possible.

FIG. 2 is a block diagram illustrating example components of IMD 12. Inthe example of FIG. 2, IMD 12 includes stimulation circuit 50,processing circuit 52, telemetry circuit 54, switching circuitry 56A and56B, sensor 58A and 58B (collectively “sensors 58”), coils 14A and 14B(collectively “coils 14”), memory 62, and power source 64. In otherexamples, IMD 12 may include a greater or fewer number of components. Insome examples, IMD 12 may not include coils 14B, switching circuitry56B, or sensor 58B, and may instead use coils 14A (and related switchingcircuitry 56A and sensor 58A) to recharge power source 64 as discussedherein. Further, in some example, IMD 12 may only utilize a plurality ofcoils 14 as discussed herein (e.g., coils that may be coupled in seriesand series opposition in response to a detected parameter) for one ofeither telemetry or recharging functions. Put differently, in someexamples, IMD 12 may include a single coil (e.g., that is not configuredto be coupled in series opposition with another coil) to providetelemetry or recharging functions.

In general, IMD 12 may comprise any suitable arrangement of hardware,alone or in combination with software and/or firmware, to perform thevarious techniques described herein attributed to IMD 12 and processingcircuit 52. In various examples, processing circuit 52 may include oneor more processors, such as one or more microprocessors, digital signalprocessors (DSPs), application specific integrated circuits (ASICs),field programmable gate arrays (FPGAs), or any other equivalentintegrated or discrete logic circuitry, as well as any combinations ofsuch components. Memory 62 may include random-access memory (RAM), readonly memory (ROM), programmable read only memory (PROM), erasableprogrammable read only memory (EPROM), electronically erasableprogrammable read only memory (EEPROM), flash memory, comprisingexecutable instructions for causing the one or more processors toperform the actions attributed to them. Memory 62 may store stimulationprograms, sense or stimulation electrode combinations, or otherinstructions that specify therapy parameter values for the therapyprovided by stimulation circuit 50 and IMD 12. Moreover, althoughprocessing circuit 52, stimulation circuit 50, and telemetry circuit 54are described as separate portions of circuitry, in some examplesprocessing circuit 52, stimulation circuit 50, and/or telemetry circuit54 may be fully or partially integrated with each other. In someexamples, processing circuit 52, stimulation circuit 50, and/ortelemetry circuit 54 correspond to individual hardware units, such asASICs, DSPs, FPGAs, or other hardware units. Similarly, though switches56 and sensors 58 are depicted as separate components, in other examplesswitches 56 and sensors 58 may be integrated into or be coupled directlyto (in the case of sensors 58) one or more of processing circuit 52,stimulation circuit 50, and telemetry circuit 54. In some examples, manycomponents of FIG. 2, such as processing circuit 52, stimulation circuit50, telemetry circuit 54, and memory 62, may be hermetically sealedwithin a housing of IMD 12.

Stimulation circuit 50 may generate and deliver electrical stimulationunder the control of processing circuit 52. In some examples, processingcircuit 52 controls stimulation circuit 50 by accessing memory 62 toselectively access and load at least one of the stimulation programs tostimulation circuit 50. For example, in operation, processing circuit 52may access memory 62 to load one of the stimulation programs tostimulation circuit 50. In such examples, relevant stimulationparameters may include a voltage amplitude, a current amplitude, a pulserate, a pulse width, a duty cycle, or the combination of electrodes 22.Processing circuit 52 may use these stimulation parameters to causestimulation circuit 50 to deliver the electrical stimulation signal.Although stimulation circuit 50 may be configured to generate anddeliver electrical stimulation therapy via one or more of electrodes 22of lead 20, stimulation circuit 50 may be configured to providedifferent therapy to patient 16. For example, stimulation circuit 50 maybe configured to deliver, e.g., configured with a pump to provide, drugdelivery therapy via a catheter. These and other therapies may beprovided by IMD 12.

Processing circuit 52 and telemetry circuit 54 may control the exchangeof information with external devices such as charging device 28 and/orexternal programmer 30 (though, as discussed herein, in some examplescharging device 28 and programmer 30 may be integrated together into asingle device). Telemetry circuit 54 may be configured for wirelesscommunication, e.g., using radio frequency protocols or inductivecommunication protocols. Telemetry circuit 54 may use coils 14A tocommunicate with programmer 30, for example. Processing circuit 52 maytransmit operational information to and receive stimulation programs ortherapy parameter adjustments from programmer 30 via coils 14A andtelemetry circuit 54. Also, in some examples, IMD 12 may communicatewith other implanted devices, such as stimulators, control devices, orsensors, via coils 14A and telemetry circuit 54. Examples of localwireless communication techniques that may be employed to facilitatecommunication between an external device and IMD 12 include RFcommunication according to the 802.11 or Bluetooth specification sets orother standard or proprietary telemetry protocols.

Though coils 14A are depicted as a single entity for purposes ofillustration, it is to be understood that coils 14A represents two ormore individual coils that may be coupled together and to telemetrycircuit 54 as described herein. Coils 14A may include two or more coilsof wire that are wrapped around or within IMD 12, or printed traces orthe like that are capable of inductive communication protocols. Coils14A may be configured to transmit or receive a signal using thecommunication techniques described above. Telemetry circuit 54 may causecoils 14A to create and transmit a signal (e.g., transmit a signal tocharging device 28 and/or programmer 30). Further, a signal received bycoils 14A (e.g., as sent by charging device 28 and/or programmer 30) maybe managed by telemetry circuit 54. Processing circuit 52 and/ortelemetry circuit 54 may cause switching circuitry 56A to couple coils14A in series to cause coils 14A to receive or transmit signals, thoughprocessing circuit 52 is described herein as controlling coupling ofcoils 14A for purposes of clarity. When switching circuitry 56A couplesall coils 14A in series, all coils 14A may be functionally wound orcoiled (both words used interchangeably herein) in a same direction witha current (e.g., a current from telemetry circuit as generated usingpower source 64) induced in the same direction through all coils 14A byan external field.

IMD 12 may include sensor 58A, which may be a measurement circuitconfigured to measure the current and/or voltage induced duringinductive electromagnetic coupling. Processing circuit 52 may use sensor58A to determine when an induced current surpasses a threshold. In someexamples, the transmitted power may be used to approximate thetemperature of IMD 12 and that of the surrounding tissue. This methodmay be used to indirectly measure the temperature of tissue in contactwith the housing of IMD 12. Alternatively, sensor 58A may be atemperature sensor that includes one or more components (e.g.,thermocouples or thermistors) configured to measure the temperature ofIMD 12. Temperature sensor 58A may be disposed internal of the housingof IMD 12, contacting the housing of IMD 12, formed as a part of thehousing of IMD 12, or disposed external of the housing of IMD 12. Asdescribed herein, temperature sensor 58B may be used to directly measurethe temperature of IMD 12 and/or tissue surrounding and/or contactingthe housing of IMD 12. While in some examples temperature sensor 58A maycontact a housing of IMD 12, in other examples temperature sensor 58Amay contact coils 14A, or both, or neither. For example, temperaturesensor 58A may be an infrared temperature sensor that is mounted on acircuit board of IMD 12 as a method of measuring temperature of thehousing of IMD 12 and/or the tissue surrounding IMD 12 withoutcontacting either the housing and/or tissue. Although a singletemperature sensor may be adequate, multiple temperature sensors mayprovide a better temperature gradient or average temperature of IMD 12.Although processing circuit 52 may continually measure temperature usingsensor 58B processing circuit 52 may conserve energy by only measuringtemperature during recharge sessions. Further, temperature may besampled at a rate necessary to calculate the cumulative thermal dose,but the sampling rate may be reduced to conserve power as appropriate.

Processing circuit 52 may modify a coupling of coils 14A using switchingcircuitry 56A in response to detected parameters from sensor 58A. Forexample, processing circuit 52 may cause switching circuitry 56A tocouple coils 14A in series opposition in response to detecting that acurrent or temperature as identified using sensor 58A surpasses athreshold. The threshold may be a predetermined threshold saved inmemory 62. The threshold may be a point at which IMD 12 and/or patient16 may experience adverse effects, or a point that is a safety marginbelow the point at which the IMD 12 and/or patient may experienceadverse effects. For example, the adverse effect point may include atemperature of IMD 12 at which patient 16 may experience some discomfortor components of IMD 12 operate with less efficiency.

Coupling coils 14A in series opposition may include coupling coils 14Asuch that a current that is induced by some of coils 14A may cancel orreduce a current that is reduce a current that is induced by theremainder of coils 14A. For example, all coils 14A may be wound orcoiled in a same direction as mounted on IMD 12, but switching circuitry56A may couple a relative input terminus of one of coils 14A to arelative output terminus of another of coils 14A to effectively causesome of coils 14A to be wound or coiled in an opposing direction toother coils 14A as experienced by a current or signal of IMD 12.

As noted above, IMD 12 may include power source 64. Power source 64 mayinclude one or more capacitors, batteries, or other energy storagedevices. Power source 64 may then deliver operating power to thecomponents of IMD 12. Power source 64 may be configured to operatethrough hundreds or thousands of discharge and recharge cycles. Powersource 64 may also be configured to provide operational power to IMD 12during the recharge process. In some examples, power source 64 may beconstructed with materials to reduce the amount of heat generated duringcharging. In other examples, IMD 12 may be constructed of materials thatmay help dissipate generated heat at power source 64 and/or rechargecoils 14B over a larger surface area of the housing of IMD 12.

Power source 64 may be rechargeable through the use of coils 14B. Coils14B, which may include two or more coils, may be capable of inductivecoupling with a primary coil (e.g., within charging device 28) that isdisposed external to patient 16. The induced electrical current may thenbe used to recharge power source 64. In this manner, the electricalcurrent may be induced in coils 14B and provided to power source 64. Theinduction may be caused by electrical current generated in the primarycoil of external charging device 28. Though recharge coils 14B aredepicted in FIG. 2 as a discrete component in relation to telemetrycoils 14A, in other examples some or all of recharge coils 14B may beused as telemetry coils 14A.

To recharge power source 64, processing circuit 52 may cause switchingcircuitry 56B to couple all coils 14B in series, such that all coils 14Bare wound or coiled in the same direction and the induced current ofeach of the coils 14B is substantially summed together before being usedto recharge power source 64. In some examples, the induced current maybe based on the selected power level (e.g., as selected by a useroperating charging device 28). The coupling between coils 14B and theexternal charging coil may be dependent upon the alignment of coils 14Band the external primary coil in charging device 28. In some examples,the coupling efficiency increases when all coils share a common axis andare in close proximity to each other. The external charging device 28and/or IMD 12 may provide one or more audible tones or visualindications of the alignment.

Alternatively, in some examples, IMD 12 may not include power source 64,but rather the power required to provide the functionality of IMD 12 maybe delivered by an induced current of coils 14B. Put differently, thecurrent induced by coils 14B in response to an electromagnetic field maybe routed to components (e.g., processing circuit 52, telemetry circuit54, stimulation circuit 50) of IMD 12 for pseudo-immediate use, such IMD12 does not include a component that is configured to store a charge forlater use. A device that is external to IMD 12 (e.g., charging device28) may need to provide the charging electromagnetic signal for theentirety of the duration for which IMD 12 will provide stimulation ormonitoring functionality in order for coils 14B to induce a sufficientamount of current for IMD 12 to provide this stimulation or monitoringfunctionality. In this example, processing circuit 52 may causeswitching circuitry 56B to couple coils 14B in series throughout thisduration, so that coils 14B may provide a consistent source of power toIMD 12.

As discussed herein, processing circuit 52 may cause switching circuitry56B to couple coils 14B in series opposition to each other, such thatsome of coils 14B are functionally wound or coiled in opposingdirections and the induced current of these coils 14B are, at least inpart, cancelled out. Processing circuit 52 may cause switching circuitry56B to couple coils 14B in series opposition in response to detectingthat an induced current of coils 14B surpasses a threshold. For example,patient 16 may undergo magnetic resonance imagining (MRI) testing, andthe resulting electromagnetic fields may cause coils 14B to induce arelatively large current that surpasses the threshold (e.g., while coils14B are coupled in series). Processing circuit 52 may detect that theinduced current surpasses the threshold, in response to which processingcircuit 52 may couple coils 14B in series opposition. As a result ofbeing coupled in series opposition, coils 14B may functionally inducelittle or no current.

IMD 12 may include one or more circuits that filter and/or transform theelectrical signal induced in coils 14B to an electrical signal capableof recharging power source 64. For example, in alternating currentinduction, IMD 12 may include a half-wave rectifier circuit and/or afull-wave rectifier circuit configured to convert alternating currentfrom the induction to a direct current for power source 64. Thefull-wave rectifier circuit may be more efficient at converting theinduced energy for power source 64. However, a half-wave rectifiercircuit may be used to store energy in power source 64 at a slower rate.In some examples, IMD 12 may include both a full-wave rectifier circuitand a half-wave rectifier circuit such that IMD 12 may switch betweeneach circuit to control the charging rate of power source 64 andtemperature of IMD 12.

Although power source 64 and recharge coils 14B are shown as containedwithin a main housing of IMD 12, at least one of these components may bedisposed outside of the main housing of IMD 12. For example, rechargecoils 14B may be disposed outside of the main housing of IMD 12 (e.g.,in an overmolding of the house) to facilitate better coupling betweenrecharge coil 14B and a charging coil of external charging device 28.Alternatively, power source 64 and/or recharge coils 70 may be locatedin a separate housing or a separate component of the same housing of IMD12. Locating coils 14B outside of a main housing of IMD 12 may improvean ability of coils 14B to receive signals without being attenuated bymaterials of the main housing (e.g., where the housing is partially orentirely metallic or some other material that blocks electromagneticfields). Further, in some examples, locating recharge coils 14Brelatively further away from the main housing of IMD 12 may increase theavailable bandwidth of frequencies with which power source 64 may berecharged.

FIGS. 3A and 3B are conceptual and schematic diagrams of coils 114A,114B (collectively “coils 114”) being coupled in series and seriesopposition, respectively. Coils 114 may be substantially similar tocoils 14 as described herein, with the exception of any differencesdescribed herein. The conceptual and schematic diagram of FIGS. 3A and3B include a portion of switching circuitry 156, which may besubstantially similar to switching circuitry 56 with the exception ofany differences described herein. Switching circuitry 156 may alter amanner in which both coils 114 are coupled relative to terminals 110A,110B (collectively, “terminals 110”) that are coupled to othercomponents and/or circuitry of IMD 12 (e.g., terminals 110 may becoupled to one or more of power source 64, processing circuit 52, ortelemetry circuit 54 of FIG. 2). Coils 114 are discussed as if they weremounted on or within IMD 12, though it is to be understood that coils114 may be mounted on other IMDs in other examples.

Coil 114A may be substantially similar to coil 114B, such that firstcurrent 116 that is induced by coil 114A may be substantially similar tosecond current 118 that is induced by coil 114B when both coils 114 areexposed to substantially similar electromagnetic fields and oriented ina substantially similar fashion. For example, both coils 114 may have asubstantially similar (e.g., functionally equal) physical dimensions,such as a substantially similar number of turns, winding radius, pitch,spacing (e.g., between loops), or the like. As used herein,substantially similar components include components that are designedand/or manufactured to be identical in purpose and/or dimensions, thoughas manufactured the components may be slightly different (e.g., as aresult of natural manufacturing imperfections). Further, coil 114A maybe wound or coiled in first direction 102 as mounted on IMD 12 and coil114B may be wound or coiled in second direction 104 as mounted on IMD12, where first direction 102 and second direction 104 are substantiallysimilar.

Coil 114A may have coil input 106A and coil output 108A, and coil 114Bmay have coil input 106B and coil output 108B. It is to be understoodthat inputs 106A, 106B (collectively, “inputs 106”) are not intended toimply a point at which signals or current always or typically flows tothe respective coils 114 to other components of IMD 12, much likeoutputs 108A, 108B (collectively “outputs 108”) are not intended toimply a point at which signals or current always or typically flows outfrom the respective coils 114 to other components of IMD 12. Rather,inputs 106 and outputs 108 are used herein to indicate respectiveterminal points of coils 114 relative to the global winding direction ofcoils, such that if a respective input 106 of a respective coil 114 iscoupled to a respective other output 108 of a respective other coil 114,a potential induced current of the two coils 114 is added togetheracross the IMD 12.

Processing circuit 52 may cause switching circuitry 156 of IMD 12 toelectrically couple coils 114 together in series to send a signal orinduce a current to recharge power source 64. For example, switchingcircuitry 156 may couple terminal 110B to input 106B of coil 114B,couple output 108B of coil 114B to input 106A of coil 114A, and coupledoutput 108A to terminal 110A, such that both coils 114 are coupled inseries. As a result of coils 114 being coupled by switching circuitry156 in series (e.g., as caused by processing circuit 52), coils 114 may“work together” to induce a current to transmit a signal. For example,coils 114 may be telemetry coils (e.g., coils 14A of FIG. 2), andtelemetry circuit 54 may cause coils 114 to transmit a signal to anexternal device such as charging device 28 or programmer 30. In someexamples, a combined capacity of both coils 114 may be greater than orequal to a capacity required to receive or transmit a signal, where acapacity of coils 114 may be a surface area of coils 114, or a number ofturns and radius of coils 114, or the like. Put differently, IMD 12 maybe configured such that a combined capacity of both coils 114 issufficient to transmit or receive a signal over a desired operationaldistance, while a single capacity of just one of coils 114 may beinsufficient. As such, as a result of switching circuitry 156 of IMD 12coupling coils 114 in series, coils 114 may be configured to transmit asignal (e.g., a signal as created by telemetry circuit 54 and routed toinput 106B or output 108A) through the combined capability of both coils114.

Conversely, coils 114 may be charging coils (e.g., coils 14A of FIG. 2),such that current that is induced by coils 114 is routed to power source64 of IMD 12. Where coils 114 are charging coils, processing circuit 52may cause switching circuitry 156 to couple coils 114 in series (e.g.,by coupling input 106A of coil 114A to output 108B of coil 114B, or bycoupling input 106B of coil 114B to output 108A of coil 114A) to addtogether a capacity of both coils 114.

Processing circuit 52 may detect that coils 114 are inducing a currentthat is above a threshold current. Processing circuit 52 and/orswitching circuitry 156 may detect that coils 114 are inducing more thana threshold current using sensor 58. For example, as described herein,sensor 58 may detect temperature (e.g., and therein detect that aninduced current has a magnitude that is sufficient to raise atemperature of the IMD 12 or surrounding tissue to above a thresholdmount), or sensor 58 may directly detect an induced current.

In response to detecting that an induced current is above a thresholdcurrent, switching circuitry 156 may couple coils 114 in seriesopposition. For example, as depicted in FIG. 3B, switching circuitry 156may couple terminal 110B to output 108B of coil 114B, couple input 106Bof coil 114B to input 106A of coil 114A, and couple output 108A toterminal 110A. As a result of this coupling, first current 116 that isinduced by coil 114A (e.g., as a result of an electromagnetic fieldcreated by charging device 28 may be substantially negated or cancelledby second current 118 induced by coil 114B as a result of first current116 of coil 114A being routed to oppose second current 118 of coil 114Bas depicted in FIG. 3B. In some examples, processing circuit 52 maycause switching circuitry 156 to couple coils 114 in series oppositionuntil sensor 58 detects that a current (e.g., first current 116 orsecond current 118) or temperature has dropped below a second threshold,in response to which processing circuit 52 may cause switching circuitry156 to couple coils 114 in series. The second threshold may be the sameas or different than the first threshold. For example, the firstthreshold at which processing circuit 52 causes switching circuitry 156to couple coils 114 in series opposition may be a first temperature, andthe second threshold at which processing circuit 52 causes switchingcircuitry 156 to couple coils 114 in series may be a second temperaturethat is relatively lower than the first temperature. Configuring theprocessing circuit 52 to cause switching circuitry 156 to couple coils114 in series subsequent to coupling coils 114 in series opposition at asecond threshold that is relatively less than a first threshold mayincrease an ability of IMD 12 to regulate a temperature and current ofIMD 12.

In other examples, whenever processing circuit 52 uses sensor 58 todetect that one or both coils 114 have induced a current that surpassesthe first threshold, processing circuit 52 may cause switching circuitry156 to couple coils 114 in series opposition for a predeterminedduration of time. For example, in response to determining that one orboth coils 114 may have induced a current that surpasses a threshold,processing circuit 52 may cause switching circuitry 156 to couple coils114 in series opposition for the subsequent 15 minutes, or hour, orother duration. In some examples, processing circuit 52 may determine aduration for which coils 114 are coupled in series opposition based on arate at which the induced current approaches and surpasses the threshold(e.g., as determined by processing circuit 52), where a relativelyfaster approach/steeper rate towards the threshold (e.g., where one orboth coils 114 induced a current that surpassed the thresholdtemperature in a relatively short period of time) results in arelatively longer duration for which coils 114 are coupled in seriesopposition.

In some examples, one coil 114 may have a relatively greater capacitythan the other coil 114. For example, coil 114A may have one more turnthan coil 114B. Configuring one coil 114A to be greater than the othercoil 114B may enable the combination of coils 114 to still induce acurrent or transmit or receive a signal when coils 114 are coupled inseries opposition, albeit at a relatively lower capacity. For example,coils 114 may be recharging power source 64, but coils 114 may inducetoo large of a current that raises a temperature of IMD 12 past thefirst threshold, such that processing circuit causes switching circuitry156 to couple coils 114 in series opposition for the subsequent twominutes (e.g., as a result of the relatively low rate at which theinduced current of coils 114 caused the temperature of IMD 12 to rise).Where coil 114A has a greater capacity than coil 114B (e.g., a 10%greater capacity as a result of an additional turn made by coil 114Arelative to coil 114B), coils 114 may still induce a current that maycause power source 64 to charge as IMD 12 cools down. Similarly, coils114 may be telemetry coils 114 implanted in patient, and coils 114 mayinduce a current that surpasses a threshold as a result of patient 16undergoing an MRI. In this example, processing circuit 52 may causeswitching circuitry 156 to couple coils 114 in series opposition, and asa result of the relatively greater capacity of coil 114A IMD 12 maystill receive and transmit signals (e.g., though potentially with arelatively reduced operational range).

FIGS. 4A and 4B are conceptual and schematic diagrams of coils 214A,214B, 214C (collectively “coils 214”) being coupled in series and seriesopposition, respectively. Coils 214 may be substantially similar tocoils 14 and coils 114 as described herein, with the exception of anydifferences described below. The conceptual and schematic diagram ofFIGS. 4A and 4B include a portion of switching circuitry 256, which maybe substantially similar to switching circuitry 56 and switchingcircuitry 156 with the exception of any differences described herein.Switching circuitry 256 may alter a manner in which both coils 214 arecoupled relative to terminals 212A, 212B (collectively, “terminals 212”)that are coupled to other components and/or circuitry of IMB 12 (e.g.,terminals 212 may be coupled to one or more of power source 64,processing circuit 52, or telemetry circuit 54 of FIG. 2). Coils 214 arediscussed as if they were integrated into IMB 12, though it is to beunderstood that coils 214 used in other IMDs in other examples.

Coil 214A may be substantially similar to coil 214B, such that coil 214Amay induce first current 216 that is substantially similar to secondcurrent 218 induced by coil 214B when uniformly exposed to anelectromagnetic field, wherein uniformly exposed includes both coils214A, 214B being oriented in a substantially similar direction such thata magnitude and direction of the electromagnetic field is substantiallyequal to both coils 214. However, coil 214C may have a substantiallysmaller capacity (e.g., as a result of a relatively smaller radius orrelatively less turns of coil 214C) than coils 214A, 214B, such thatcoil 214C may induce a substantially smaller third current 220 as coils214A, 214B when exposed to the electromagnetic field. Coil 214A may bewound or coiled in first direction 202 as mounted on IMD 12, coil 214Bmay be physically wound/coiled in second direction 204 as mounted on IMD12, and coil 214C may be wound/coiled direction in a third direction 210as mounted on IMD 12, where first direction 202, second direction 204,and third direction 210 are substantially similar.

Coil 214A may have coil input 206A and coil output 208A, coil 214B mayhave coil input 206B and coil output 208B, and coil 214C may have coilinput 206C and coil output 208C. It is to be understood that inputs206A, 206B, 206C (collectively, “inputs 206”) are not intended to implya point at which signals or current flows to the respective coils 214from other components of IMD 12, much like outputs 208A, 208B, 208C(collectively “outputs 208”) are not intended to imply a point at whichsignals or current flows out from the respective coils 114 to othercomponents of IMD 12. Rather, inputs 206 and outputs 208 are used hereinto indicate respective terminal points of coils 214 relative to theglobal winding direction of coils, such that if a respective input 206of a respective coil 214 is coupled to a respective other output 208 ofa respective other coil 214, a potential induced current of the twocoils 214 is added together.

Processing circuit 52 may cause switching circuitry 256 to couple coils214 in series to send a signal or induce a current. For example,processing circuit 52 may cause switching circuitry 256 to coupleterminal 212B to input 206C of coil 214C, couple output 208C of coil214C to input 206B of coil 214B, couple output 208B of coil 214B toinput 206A of coil 114A, and couple output 208A of coil 214A to terminal212A, such that all coils 114 are coupled in series. As a result of allcoils 214 being coupled in series, all coils 214 may function as asingle coil wound or coiled in a single direction to induce a current orto transmit or receive a signal.

Processing circuit 52 and/or switching circuitry 256 may detect that oneor more coils 214 are inducing a current that is above a thresholdcurrent as described herein. In response to detecting that an inducedcurrent is above a threshold current, switching circuitry 256 may couplesome of coils 214 in series opposition. For example, as depicted in FIG.4B, switching circuitry 256 may couple input 206C of coil 214C to input206A of coil 214A. As a result of this coupling, first current 216induced by coil 214A (e.g., as a result of an electromagnetic fieldcreated by charging device 28) may be substantially negated or cancelledby second current 218 induced by coil 214B that is routed tosubstantially oppose first current 216, leaving only third current 220induced by coil 214C.

In other examples, there may be more than three coils 214 that havedifferent relative capacities. For example, the combined capacity ofcoils 214B and coil 214C may be substantially equal to coil 214A, suchthat processing circuit 52 may couple both coil 214B and coil 214C to bein series opposition to coil 214A in order to effectively cancel out anet induced current across all coils. In this example, coil 214B mayhave 30% of the capacity of coil 214A, while coil 214C has 20% of thecapacity of coil 214A. In this example, processing circuit 52 mayeffectively ramp up or ramp down an amount of potential induced currentthat is cancelled by the coupling of coils 214 in response to a detectedcurrent or temperature.

For example, processing circuit 52 may couple both coil 214B and coil214C in series opposition to coil 214A in response to detecting that IMD12 has rapidly approached and surpassed a threshold temperature whenrecharging power source 64, such that substantially no current isinduced across coils 214. For example, where second current 218 andthird current 220 summed to a substantially similar magnitude as firstcurrent 216, the coupling of FIG. 4B may result in substantially nocurrent being induced across all coils 214. Once processing circuit 52detects (e.g., using sensor 58) that IMD 12 has cooled to a secondtemperature (e.g., that is below the first threshold), processingcircuit 52 may cause switching circuitry 256 to couple coil 214C to bein series with coil 214A while coil 214B is in series opposition withboth coil 214A and coil 214C. For example, switching circuitry 256 maycouple coil 214B to be in series opposition with both coil 214A and coil214C by coupling terminal 212B with input 206C of coil 214C, couplingoutput 208C of coil 214C with output 208B of coil 214B, coupling input206B of coil 214B with input 206A of coil 214A, and coupling output 208Aof coil 214A with terminal 212A. Alternatively, switching circuitry 256may couple coil 214B to be in series opposition with both coil 214A andcoil 214C by coupling terminal 212B with input 206C of coil 214C,coupling output 208C of coil 214C with input 206A of coil 214A, couplingoutput 208A of coil 214A with output 208B of coil 214B, and couplinginput 206B of coil 214B with terminal 212A. Other ways of coupling coils214 together to configure coil 214B to be in series opposition with bothcoil 214A and coil 214C are also possible.

Using such configurations, 20% of the possible capacity of coils 214 isused to induce current to recharge power source 64. Subsequent to this,processing circuit 52 may detect that IMD has cooled to a thirdtemperature (e.g., that is below the second temperature), in response towhich processing circuit 52 may cause coil 214A and coil 214B to be inseries while coil 214C is in series opposition with both, such as bycoupling coil input 206C of coil 214C to coil input 206B of coil 214Band coupling coil output 208B of coil 214B to coil input 206A of coil214A. Other ways of selectively coupling coils 214 are possible toachieve this result.

According to such a configuration, 30% of the capacity of coils 214 isused to induce current to recharge power source 64. Subsequent to this,processing circuit 52 may detect that IMD has cooled to a fourthtemperature (e.g., that is below the third temperature) in response towhich all coils 214 are coupled in series such that substantially all ofthe capacity is used to induce current for recharging power source 64.This may be accomplished, for instance, using a configuration such asshown in FIG. 4A, although other configurations are possible.

FIGS. 5A-5E are conceptual and perspective diagrams of example coils.FIG. 5A depicts two coils 314A, 314B (collectively “coils 314”) mountedon housing 310 of IMD 312. IMD 312 may be substantially to IMDS 12 ofFIGS. 1A and 1B. The general shape of housing 310 is depicted forpurposes of illustration only, as housing 310 may be any shape thatenables IMD 312 to function as required. For example, in other exampleshousing 310 may be shaped to include a connection header (e.g., toreceive one or more leads 20) that extends from housing 310.

As depicted in FIG. 5A, coils 314 of IMD 312 are secured to outersurface 318 of housing 310 of IMD 312. In certain examples, housing 310may be partially or entirely metallic, such that housing 310 may have anability to block some or all electromagnetic fields and/or signals thatare created by or intended for coils 314. In such examples, it may beadvantageous to secure coils 314 to outer surface 318 of housing 310,such that these coils 314 have an unobstructed path within whichelectromagnetic fields may be received or transmitted.

Coils 314 may be secured within a recess 316 of housing 310. Recess 316may extend into housing 310 along a perimeter of housing 310. Recess 316may have a depth that is greater than a cross-sectional width of coils360. In some examples, an overmold may cover coils 314 and housing 310once coils 314 are secured to housing 310. The overmolding may serve toencapsulate the housing 310 and coils 314 and reduce or eliminate sharpcorners or edges of housing 310 or coils 314 that may tear or otherwiseirritate tissue adjacent IMD 312 once IMD 312 is implanted into patient16.

FIGS. 5B and 5C illustrate two conceptual and schematic diagrams ofcoils 414A-414D (collectively “coils 414”) that can be placed onrespective frames 402A and 402B (collectively “frames 402”) of an IMD,such as IMD 12. Though coils 414 are depicted as solid objects (e.g.,without individual windings) for purposes of clarity; it is to beunderstood that coils 414 may include any number of windings in anyconfiguration that may execute the functions described herein. The coils414 may be substantially similar to coils 14, 114, 214, or 314 asdescribed herein. In certain examples, coils 414 may be directly placedon frames 402, whereas in other examples coils 414 may be placed onframes 402 within individual respective housings.

Frames 402 may include a die stack for an integrated circuit of IMD 12.For example, frames 402 may be a die stack that attaches directly to aprinted circuit board (PCB) of IMD 12, where the PCB includes one ormore of stimulation circuit 50, processing circuit 52, telemetry circuit54, memory 62, switching circuitry 56, or sensors 58. In some examples,coils 414 may be stacked on respective frames 402. For example, asdepicted in FIG. 5B, coils 414A and 414B may be stacked (rather thancoplanar) as they are received by frame 402A. In other examples, coils414 may be nested and/or coplanar as they are received by respectiveframes. For example, as depicted in FIG. 5C, inner coil 414C may fitwithin outer coil 414D as received on frame 402B, such that coils 414are nested and coplanar as received by frame 402B. Frames 402 may besized differently to receive coils 414 in a stacked or coplanarconfiguration. For example, as depicted, frame 402A may be relativelydeeper to receive coils 414 in the stacked configuration, and frame 402Bmay be relatively wider to receive coils 414 in the nested or coplanarconfiguration.

In some examples, frames 402 may include a plurality of pads 406A-406D(collectively “pads 406”) along a respective perimeter 404A, 404B(collectively “perimeters 404”) of frame 402. Pads 406 may be metallizedor otherwise conductive. Conductive traces that are on or embeddedwithin frame 402 may electrically couple some pads 406 to coils 414(e.g., as controlled by switching circuitry 56), while other pads 406 offrame 402 be configured to secure frame 402 and/or coils 414 to PCB. Forexample, where IMD 12 includes two coils 414 (e.g., as in FIGS. 3A and3B), frame 402 may include two connective metallic pads 406 per coil414, where two connective pads 406 connect (through conductive tracesand switching circuitry) to an input and output of first coil 414A, andtwo other connective pads 406 connect (through conductive traces andswitching circuitry) to an input and output of second coil 414B. WhereIMD 12 contains more coils 414, frame 402 may include more respectiveconnective pads 406 to couple to the respective more coils 414.

Pads 406 may be located on lips 408A, 408B (collectively “lips 408”) ofperimeters 404 and/or pads 406 may be located on walls 410A, 410B(collectively “walls 410”) of perimeters 404. Pads 406 along perimeters404 of frames 402 may be arranged at different locations along lips 408and walls 410 depending upon the respective configurations of coils 414.For example, where coils 414 are stacked as depicted in FIG. 5B, somepads 406 such as pad 406B may be located along lip 408A of perimeter404A. On this lip 408A, pads 406 such as pad 406B may secure orelectrically couple with a “bottom” coil 414B once stacked coils 414 arereceived by frame 402A. Similarly, some pads 406 such as pad 406A may belocated along wall 410A of perimeter 404A, where these pads 406 such aspad 406A may secure or electrically couple with a “top” coil 414A oncestacked coils 414 are received by frame 402A. Alternatively, where coils414 are nested or coplanar as depicted in FIG. 5C, pads 406 may mostlyor exclusively be located on lip 408B on perimeter 404B (e.g., such thatno pads 406 are located on wall 410B of perimeter 404B) within two ormore rows, with a respective row for each coil 414. In this manner, somepads 406 such as pad 406C may align with an “inner” coil 414C and otherpads 406 such as pad 406D may align with an “outer” coil 414D to secureor be electrically coupled with respective coils 414 as describedherein.

In some examples, additional pads 406 may be located on bottom surface412 of frame 402, or the same pads 406 may extend through to bottomsurface 412 of frame 402, where bottom surface 412 is a surface of lip408. From bottom surface 412, pads 406 may connect to adjoiningcircuitry, such as the circuitry described herein (e.g., processingcircuitry, telemetry circuitry, or the like). In this way, coils 414 maybe coupled through pads 406 to circuitry that is adjacent to frame 402.By configuring pads 406 to extend through frame 402 to electricallycouple coils 414 to respective circuitry, an IMD 12 may reduce oreliminate the need for additional connectors extending through IMD 12.

FIG. 5D illustrates a conceptual and schematic diagram of coil 514 thatis a printed trace upon surface 500 of component 502 of an IMD, such asIMD 12. Coil 514 may be substantially similar to coils 14, coils 114,coils 214, coils 314, or coils 414 as described herein. Component 502may be a housing of an IMD, such that surface 500 is an outer surface ofthe IMD and two or more coils 514 are printed on opposing sides of thehousing. In this example, coils 514 may be covered with an overmoldingonce IMD is assembled and coils 514 are printed on the housing. In otherexamples, component 502 may be an internal feature of the IMD (e.g.,such that component 502 is encapsulated within a housing of the IMD),with different coils 514 printed on different surfaces or all on surface500 of component 502. In such examples, coils 514 may all be within oneplane, or coils 514 may define a 3D structure across planes.

FIG. 5E illustrates a conceptual and schematic diagram of two coils614A, 614B (collectively “coils 614”). Coils 614 may be substantiallysimilar to coils 14, coils 114, coils 214, coils 314, coils 414, orcoils 514 as described herein, with the exception of any differencesdescribed below. As depicted, coils 614 may include two helical coilsthat extend around separate axes. Coils 614 may be located anywherewithin a housing of an IMD, or coils 614 may be secured within anovermolding surrounding a housing. In some examples, coils 614 may sharea common axis, i.e., be coaxial. In certain examples where coils 614 arecoaxial (e.g., as encased within a cable), first coil 614A may be withinsecond coil 614B (e.g., such that first coil 614A has a greater radiusthan second coil 614B) even as first coil 614A has a substantiallyequivalent capacity as second coil 614B as a result of first coil 614Ahaving relatively fewer turns than second coil 614B.

FIG. 6 is a flowchart illustrating a method of coupling coils inresponse to a detected parameter that indicates a magnitude of aninduced current of a received signal. FIG. 6 is described predominantlywith reference to elements of FIGS. 3A and 3B, with some reference toelements of FIGS. 1-2, though the method of FIG. 6 may be executed withother coils and other IMDs in other examples. Coils 114A and 114B of IMD12 may be coupled in series (600). Processing circuit 52 may causeswitching circuitry 156 to couple coils 114 in series. Coupling coils114 in series may include coupling coils 114 such that both coils 114are functionally wound or coiled in a same direction as coupled tocomponents of IMD 12 (e.g., such that currents that are induced by coils114 will be summed together on IMD 12 rather than cancelling each otherout). Processing circuit 52 may cause switching circuitry 156 to couplecoils 114 in series so that coils 114 may recharge power source 64(e.g., with recharge signal) and/or send/receive telemetry signals.

In some examples, processing circuit 52 may cause switching circuitry156 to couple coils 114 in series whenever processing circuit 52 doesnot sense a parameter (e.g., a temperature or current) that indicatesthat coils 114 are inducing a current that is over a threshold. Putdifferently, processing circuit 52 may cause switching circuitry 156 tocouple coils 114 in series as a “default” state, such that processingcircuit 52 substantially only temporarily (e.g., for a predeterminedperiod of time or until a predetermined condition is met) causesswitching circuitry 156 to couple coils 114 in a configuration otherthan in series.

Processing circuit 52 may detect that a parameter indicates that amagnitude of an induced current is greater than a threshold (602).Processing circuit 52 may use sensors 58 to determine that the parameterindicates that the magnitude of the induced current is greater than thethreshold. For example, the parameter may be a temperature, and sensors58 may include temperature sensors that are configured to identifytemperatures of a portion of IMD 12 or tissue surrounding IMD 12, suchthat processing circuit 52 is configured to determine that aparameter/temperature indicates that the magnitude of the inducedcurrent is greater than a predetermined threshold amount as a result ofa rising temperature of IMD 12 and/or surrounding tissue. Alternatively,the parameter may be a current, voltage, or a strength of the electricfield, and sensors 58 may include current, voltage, or electric fieldstrength sensors that are configured to pseudo-directly identify acurrent induced across coils 114.

Processing circuit 52 electrically couples coils 114 in seriesopposition in response to determining that the parameter indicates thatthe magnitude of the induced current is higher than a threshold (604).Processing circuit 52 may cause switching circuitry 156 to couple coils114 in series opposition. Coupling coils 114 in series opposition mayinclude coupling coils 114 to components of IMD 12 such that coils 114are effectively wound or coiled in opposite directions, such that acurrent induced over both coils 114 may be effectively cancelled. Insome examples, coils 114 are physically disparate, such that first coil114A has a relatively greater capacity to induce a current than secondcoil 114B. For example, first coil 114A may have an extra turn or anincreased radius or the like in comparison to coil 114B, such thatcoupling coils 114 in series opposition results in a total inducedcurrent that is proportional to the amount that the two coils 114 arephysically disparate (e.g., only the additional turn of coil 114A isfunctionally realized during the process of inducing a current).

FIG. 7 is a flowchart illustrating a method of coupling three or morecoils in response to a detected magnitude of a received signal. FIG. 7is described predominantly with reference to FIGS. 4A and 4B, with somereference to FIGS. 1-2, though the method of FIG. 7 may be executed withany of the example coils and IMDs described herein. All coils 214 may becoupled in series (650). As used herein, coils 214 may include firstcoil 214A of a first capacity, second coil 214B of a second capacity,and third coil 214C of a third capacity, where none of coils 214 havethe same capacity yet the sum of the second and third capacity are equalto the first capacity (e.g., coil 214A has 50% of capacity of all coils214, coil 214B has 35% of the capacity of all coils, and coil 214C has15% of the capacity of all coils 15%). Processing circuit 52 may causeswitching circuitry 256 to couple coils 214 in series. Coupling coils214 in series may include coupling coils 214 such that all coils 214 arefunctionally wound or coiled in a same direction as coupled tocomponents of IMD 12 (e.g., such that currents that are induced by coils214 will be summed together on IMD 12 rather than cancelling each otherout).

Processing circuit 52 may detect that a magnitude of an induced currentas induced across the three coils 214 is great enough to raise atemperature to above a first threshold (652). Processing circuit 52 mayuse sensors 58 to determine a magnitude of the induced current. Sensors58 may include temperature sensors. In other embodiments, a differentparameter may be measured to determine current is too large, such ascurrent itself, a voltage across a resistive element, or an electricfield strength. Thus, while the following describes use of temperatureto trigger reconfiguring coils, it will be understood other types ofparameters could be used in addition or as an alternative totemperature. In response to determining that the induced current ishigher than a threshold, processing circuit 52 may cause switchingcircuitry 256 to couple coils 214 in series opposition such that amaximum amount of capacity is internally opposed (654). For example,processing circuit 52 may cause switching circuitry 256 to couple firstcoil 214A in series opposition with both second coil 214 and third coil214C, such that an induced current is substantially brought to zeroacross all coils 214 (e.g., as a result of an induced current of firstcoil 214A substantially cancelling an induced current of second coil214B and third coil 214C).

Processing circuit 52 may continue monitoring a temperature or otherparameter of IMD 12 and/or surrounding tissues of patient 16 todetermine if the temperature or other parameter drops below the firstthreshold (656). In some examples, processing circuit 52 continuemonitoring a temperature of IMD 12 and/or surrounding tissue of patient16. For example, processing circuit 52 may determine a temperature everyfew seconds, or every minute, or sensor 58 may be configured to notifyprocessing circuit 52 if the detected temperature. As indicated on FIG.7, processing circuit 52 may pseudo-continually monitor a temperature ofIMD 12 and/or patient 16 tissue until a temperature drops below thefirst threshold. In some examples, if processing circuit 52 detects thatIMD 12 and/or patient 16 tissue has not dropped below the firstthreshold for a predetermined duration, processing circuit 52 may causetelemetry circuit 54 to send an alarm notification using coils 214(e.g., by momentarily coupling coils 214 in series to enable an outgoingtransmission before recoupling coils 214 in series opposition as inoperation 654).

Processing circuit 52 may detect that the temperature of IMD 12 and/orsurrounding tissue has dropped below the first threshold, in response towhich processing circuit 52 may couple coils 214 such that relativelyless capacity of coils 214 is cancelled (660). For example, processingcircuit 52 may couple coils 214 such that first and third coil 214A,214C are in series with each other and second coil 214 is in seriesopposition, such that, using the example above, 65% of the capacity ofcoils 214 is inducing a capacity for IMD 12.

In response to coupling coils 214 such that relatively less capacity iscancelled across coils 214, processing circuit 52 may determine whethera detected temperature has dropped below a second threshold (662). Thesecond threshold may be lower than the first threshold, such that thetemperature dropping below first the first threshold (656) followed bydropping below the second threshold (662) indicates a continued trend ofcooling. If processing circuit 52 determines that the temperature hasdropped below the second threshold, processing circuit 52 may couple allcoils 214 in series (650). Conversely, if the measured temperature isnot below the second temperature, processing circuit 52 may determinewhether the measured temperature has raised above the first temperature(664). If the temperature of IMD 12 and/or surrounding tissue has raisedabove the first temperature, processing circuit 52 may again couplecoils 214 in a configuration to block a maximum capacity of coils 214(654), after which processing circuit 52 may monitor if coils drop belowthe first temperature (656, 658) as discussed herein. Alternatively, ifprocessing circuit 52 determines that temperature is above the secondthreshold but below the first threshold, processing circuit 52 maycontinue monitoring the temperature (668). In this way, processingcircuit 52 may be configured to dynamically measure a temperature of IMD12 and accordingly alter which coils 214 are in series with each other,therein increasing or decreasing an amount of induced current tomodulate a capacity of coils 214 while simultaneously regulating atemperature of IMD 12 and/or surrounding tissue of patient 16.Configuring IMD 12 such that processing circuit 52 may dynamically causeswitching circuitry 256 to couple coils 214 in series and seriesopposition and therein increase or decrease an amount of induced currentmay reduce an amount of stress that is placed on components of IMD 12and increase an ability to promote the comfort of patient 16 as a resultof IMD 12.

It is to be understood that the example method as depicted in FIG. 7 ofprocessing circuit 52 coupling three or more coils 214 in series orseries opposition in response to a detected magnitude of a receivedsignal is for purposes of illustration, as in other examples processingcircuit 52 may couple three or more coils 214 together in a differentmanner. For example, processing circuit 52 may couple three or morecoils 214 together according to more or less operations than aredepicted in FIG. 7, or processing circuit 52 may couple three or morecoils 214 together using similar operations as are depicted in FIG. 7that are executed in a different order.

One example of this may include the response of processing circuit 52 todetecting a temperature that is higher than a threshold (e.g., as at652). For example, in response to detecting a temperature that is higherthan a threshold when coils 214 are coupled in series, processingcircuit 52 may initially couple less than the maximum capacity of coils214 in series opposition. For example, processing circuit 52 mayincrementally increase a capacity of the set of coils 214 that iscoupled in series opposition as sensors 58 detect that a parameter keepsrising above one or more thresholds, or processing circuit 52 mayincrementally increase a capacity that is coupled in series oppositionas sensors 58 detect that a parameter remains above one or morethresholds. In this way, as the parameter either continues to rise orotherwise remains above the threshold, processing circuit 52 may couplecoils 214 from in-series, to only some coils 214 in-series, to a maxcapacity of coils 214 in series opposition, or otherwise increase theportion of coils that are coupled in series opposition.

For another example of a different manner in which coils 214 may becoupled in series or series opposition, in some examples processingcircuit 52 may use many thresholds that relate to many parameters tomodify a coupling of coils 214 (e.g., rather than only using temperatureas measured by a temperature sensor as discussed in the example methodof FIG. 7). For example, IMD 12 may include multiple sensors 58 thatdetect multiple parameters of coils 214, such as a first sensor thatdetects current, a second sensor that detects voltage, and a thirdsensor that detects temperature. In this example, processing circuit 52may use detected parameters of each of the first sensor, second sensor,and third sensor when coupling coils 214 in series or series opposition,whether by using different sensors at different times, only altering acoupling of coils 214 in response to two or more of the sensorsdetecting a value that satisfies a threshold, or the like.

This may include processing circuit 52 modifying a manner in which coils214 are coupled in response to at least two of the three sensorsdetecting a parameter that surpasses a respective threshold. Forexample, processing circuit 52 may be configured to detect but not reactto the first sensor sensing that an induced current satisfies a currentthreshold (e.g., as an induced current may momentarily spike andsubsequently drop in a way that does not necessitate any coils 214 beingcoupled in series opposition). Further, processing circuit 52 may beconfigured to couple at least some coils 214 in series opposition inresponse to detecting that the third sensor senses a correlatingincrease in temperature that satisfies a temperature threshold while thefirst sensor is still sensing that the induced current satisfies thecurrent threshold (e.g., as, where the first sensor is no longer sensingthat the induced current satisfies the current threshold, it is probablethat the temperature sensor will sense a corresponding temperature dropbelow the temperature threshold). In this way, processing circuit 52 maybe configured to use multiple sensors 58 to cross-check multiple sensedparameters to verify that the sensed parameter values warrant a responseto potentially eliminate “false positives” (e.g., situations where aparameter of IMD 12 temporarily and incorrectly indicates that couplingcoils 214 in series opposition reduces a chance of a negative effect, asthe negative effect would not have been realized either way).

Alternatively, or additionally, processing circuit 52 may use differentparameters as sensed by different sensors 58 in different conditions tocouple coils 214 in series or series opposition. For example, somesensors 58 may be more or less accurate in different ranges of theirrespective parameters, such that processing circuit 52 may use differentsensors 58 to determine how to couple coils 214 in response todetermining a respective condition of coils 214 (e.g., where thecondition may include a temperature, voltage, or current of coils 214,as examples). This may include primarily or exclusively using a sensorwhen that sensor is within its peak accuracy range. Additionally, oralternatively, this may include never or sparingly using a sensor whenthat sensor is within a low accuracy range.

This disclosure is primary directed to coupling coils in series orseries opposition to alter an amount of current that is induced by thecoils when the coils are exposed to an electromagnetic field. However,one or more aspects of this disclosure may also be applicable togenerally coupling coils in different configurations to alter aneffective coil capacity of an IMD for different applications. Forexample, aspects of this disclosure may be applicable to effectivelyincrease or decrease an effective operating range of an antenna of anIMD.

Various examples have been described. These and other examples arewithin the scope of the following claims.

The invention claimed is:
 1. An implantable medical device comprising:an implantable medical housing; a processing circuit within theimplantable medical housing; a first coil configured to wirelesslyreceive a signal and secured to the implantable medical device; a secondcoil configured to wirelessly receive the signal and secured to theimplantable medical device; switching circuitry within the housing,wherein the processing circuit is configured to cause the switchingcircuitry to selectably couple the first coil to the second coil eitherin series such that the first coil is coiled in a same direction as adirection in which the second coil is coiled or in series oppositionsuch that the first coil is coiled in an opposite direction as thedirection in which the second coil is coiled; and a sensor configured tosense a parameter that indicates a magnitude of an induced current thatis induced over the first coil and the second coil as a result ofreceiving the signal, wherein the parameter is at least one oftemperature, voltage, or current.
 2. The implantable medical device ofclaim 1, wherein the processing circuit is configured to cause theswitching circuitry to selectably couple the first coil to the secondcoil either in series or in series opposition based on the sensedparameter.
 3. The implantable medical device of claim 1, furthercomprising a power supply for the implantable medical device, whereinthe signal is a charging signal, and wherein the first coil and thesecond coil are configured to provide power from the charging signal tothe power supply when the first coil is coupled to the second coil inseries.
 4. The implantable medical device of claim 1, wherein the firstcoil has a substantially similar radius and amount of turns as a radiusand amount of turns of the second coil, such that when coupled in seriesopposition the signal received by the first coil is substantiallycancelled by the signal received by the second coil.
 5. The implantablemedical device of claim 1, wherein the first coil and the second coilare coiled coaxially.
 6. The implantable medical device of claim 1,wherein the first coil and the second coil are stacked.
 7. Theimplantable medical device of claim 1, wherein the first coil and thesecond coil are coplanar.
 8. The implantable medical device of claim 1,wherein the first coil and the second coil are configured to togethersend a telemetry signal when coupled in series.
 9. The implantablemedical device of claim 1, wherein the first coil has at least one ofrelatively more turns or a relatively greater radius than a number ofturns or a radius of the second coil, such that the first coil has arelatively greater capacity to induce current than the second coil whenboth the first coil and the second coil are uniformly exposed to anelectromagnetic field.
 10. The implantable medical device of claim 1,further comprising a third coil, wherein: the processing circuit isconfigured to cause the switching circuitry to selectably couple thefirst coil to the second coil and the third coil either in series suchthat the first coil is coiled in the same direction as the direction inwhich the second coil is coiled and a direction in which the third coilis coiled or in series opposition such that the first coil is coiled inan opposite direction as the direction in which the second coil iscoiled and the direction in which the third coil is coiled, and theprocessing circuit is configured to cause the switching circuitry toselectably couple the first coil to the second coil and the third coileither in series or in series opposition in response to detectedmeasurements of a parameter that indicates a magnitude of an inducedcurrent that is induced over the first coil, the second coil, and thethird coil.
 11. The implantable medical device of claim 1, wherein theparameter is a temperature of components of the implantable medicaldevice, wherein the processing circuit is configured to cause theswitching circuitry to couple the first coil to the second coil inseries opposition in response to the detected temperature rising above athreshold temperature.
 12. The implantable medical device of claim 1,wherein the parameter is a current measured across at least one of thefirst coil or the second coil, wherein the processing circuit isconfigured to cause the switching circuitry to couple the first coil tothe second coil in series opposition in response to the detected currentrising above a threshold current.
 13. A method of managing coils of animplantable medical device comprising: coupling, by switching circuitryof the implantable medical device as caused by a processing circuit ofthe implantable medical device, a first coil secured to the implantablemedical device to a second coil secured to the implantable medicaldevice in series such that the first coil is coiled in a same directionas a direction in which the second coil is coiled, wherein both thefirst coil and the second coil are configured to wirelessly receive asignal; receiving, by both the first coil and the second coil, thesignal; detecting, by the processing circuit, that a parameter thatindicates a magnitude of an induced current that is induced over thefirst coil and the second coil as a result of receiving the signalsurpasses a predetermined threshold; and coupling, by the switchingcircuitry of the implantable medical device as caused by the processingcircuit, the first coil and the second coil in series opposition suchthat the first coil is coiled in an opposite direction as the directionin which the second coil is coiled.
 14. The method of claim 13, furthercomprising detecting, by the processing circuit, that the parameter thatindicates the magnitude of the induced current surpasses thepredetermined threshold using a sensor configured to measure a combinedinduced current of the first coil and the second coil.
 15. The method ofclaim 13, further comprising detecting, by the processing circuit, thatthe parameter that indicates the magnitude of the induced currentsurpasses the predetermined threshold using one or more thermocouples orthermistors configured to measure a temperature of the implantablemedical device upon receiving the signal, wherein the predeterminedthreshold is a threshold temperature.
 16. The method of claim 13,wherein the predetermined threshold is a first predetermined threshold,further comprising: detecting, by the processing circuit, that theparameter that indicates the magnitude of the induced current dropsbelow a second predetermined threshold; and coupling, by the switchingcircuitry of the implantable medical device as caused by the processingcircuit, the first coil and the second coil in series such that thefirst coil is coiled in the same direction as the direction in which thesecond coil is coiled.
 17. The method of claim 16, wherein the firstpredetermined threshold is of a relatively greater magnitude than thesecond predetermined threshold.
 18. The method of claim 13, wherein theimplantable medical device includes a third coil that is secured to theimplantable medical device and configured to wirelessly receive thesignal, wherein coupling the first coil to the second coil in seriesfurther comprises coupling the third coil in series with the first coiland the second coil such that such that the first coil is coiled in thesame direction as the direction in which the second coil is coiled and adirection in which the third coil is coiled, wherein detecting that theparameter that indicates the magnitude of the induced current surpassesthe predetermined threshold further comprises detecting that theparameter that indicates the magnitude of the induced current that isinduced over the first coil, the second coil, and the third coilsurpasses the predetermined threshold, and wherein coupling the firstcoil and the second coil in series opposition further comprises couplingthe third coil in series opposition with the first coil such that thefirst coil is coiled in an opposite direction as the direction in whichthe second coil is coiled and the direction in which the third coil iscoiled, such that the received signal is effectively cancelled acrossthe first coil, the second coil, and the third coil.
 19. The method ofclaim 18, wherein the predetermined threshold is a first predeterminedthreshold, further comprising: detecting, by the processing circuit,that the parameter that indicates the magnitude of the induced currenthas fallen to a second predetermined threshold that is less than thefirst predetermined threshold; and coupling, by the switching circuitryof the implantable medical device as caused by the processing circuit inresponse to detecting that the parameter that indicates the magnitude ofthe induced current has fallen to the second predetermined threshold,the second coil in series with the first coil and in series oppositionwith the third coil, such that a first amount of the received signal iseffectively cancelled across the first coil, second coil, and the thirdcoil.
 20. The method of claim 19, further comprising: detecting, by theprocessing circuit, that the parameter that indicates the magnitude ofthe induced current has fallen to a third predetermined threshold thatis less than the second threshold; and coupling, by the switchingcircuitry of the implantable medical device as caused by the processingcircuit in response to detecting that the parameter that indicates themagnitude of the induced current has fallen to the third threshold, thethird coil in series with the first coil and the second coil in seriesopposition with the first coil and the third coil, such that a secondamount of the received signal is effectively cancelled across the firstcoil, second coil, and the third coil, wherein the second amount is lessthan the first amount.
 21. The method of claim 20, further comprising:detecting, by the processing circuit, that the parameter that indicatesthe magnitude of the induced current has fallen to a fourthpredetermined threshold that is less than the third threshold; andcoupling, by the switching circuitry of the implantable medical deviceas caused by the processing circuit, the first coil, the second coil andthe third coil in series to one another such that substantially none ofthe received signal is canceled across the first coil, the second coil,and the third coil.
 22. An implantable medical device comprising: animplantable medical housing; a processing circuit within the implantablemedical housing; one or more leads configured to extend from theimplantable medical housing and be implanted into a brain of a patient;one or more electrodes at a distal end of the one or more leads that areconfigured to deliver electrical stimulation to the brain of thepatient; a stimulation circuit configured to generate the electricalstimulation; a power supply configured to provide power for thegeneration of the electrical stimulation; switching circuitry that iselectrically coupled to the processing circuit; a first coil that iscoupled through the switching circuitry to the power supply andconfigured to wirelessly receive a charging signal; a second coil thatis coupled through the switching circuitry to the power supply andconfigured to wirelessly receive the charging signal, wherein theprocessing circuit is configured to cause the switching circuitry toselectably couple the first coil to the second coil either in seriessuch that the first coil is coiled in a same direction as a direction inwhich the second coil is coiled or in series opposition such that thefirst coil is coiled in an opposite direction as the direction in whichthe second coil is coiled; and a sensor configured to sense a parameterthat indicates a magnitude of an induced current that is induced overthe first coil and the second coil as a result of receiving the signal,wherein the parameter is at least one of temperature, voltage, orcurrent.
 23. The implantable medical device of claim 22, furthercomprising a third coil, wherein: the processing circuit is configuredto cause the switching circuitry to selectably couple the first coil tothe second coil and the third coil either in series such that the firstcoil is coiled in the same direction as the direction in which thesecond coil is coiled and a direction in which the third coil is coiledor in series opposition such that the first coil is coiled in anopposite direction as the direction in which the second coil is coiledand the direction in which the third coil is coiled; and the processingcircuit is configured to cause the switching circuitry to couple thefirst coil to the second coil and the third coil either in series or inseries opposition in response to detected measurements of a parameterthat indicates a magnitude of an induced current that is induced overthe first coil, the second coil and the third coil.